java(1)java(1)Name
java - the Java application launcher
SYNOPSIS
java [ options ] class [ argument ... ]
java [ options ] -jar file.jar [ argument ... ]
options
Command-line options.
class
Name of the class to be invoked.
file.jar
Name of the jar file to be invoked. Used only with -jar.
argument
Argument passed to the main function.
DESCRIPTION
The java tool launches a Java application. It does this by starting a
Java runtime environment, loading a specified class, and invoking that
class's main method.
The method must be declared public and static, it must not return any
value, and it must accept a String array as a parameter. The method
declaration must look like the following:
public static void main(String args[])
By default, the first non-option argument is the name of the class to
be invoked. A fully-qualified class name should be used. If the -jar
option is specified, the first non-option argument is the name of a JAR
archive containing class and resource files for the application, with
the startup class indicated by the Main-Class manifest header.
The Java runtime searches for the startup class, and other classes
used, in three sets of locations: the bootstrap class path, the
installed extensions, and the user class path.
Non-option arguments after the class name or JAR file name are passed
to the main function.
OPTIONS
The launcher has a set of standard options that are supported on the
current runtime environment and will be supported in future releases.
In addition, the current implementations of the virtual machines sup‐
port a set of non-standard options that are subject to change in future
releases.
Standard Options-client
Select the Java HotSpot Client VM. A 64-bit capable jdk currently
ignores this option and instead uses the Java Hotspot Server VM.
For default VM selection, see Server-Class Machine Detection @
http://docs.oracle.com/javase/7/docs/tech‐
notes/guides/vm/server-class.html
-server
Select the Java HotSpot Server VM. On a 64-bit capable jdk only
the Java Hotspot Server VM is supported so the -server option is
implicit.
For default VM selection, see Server-Class Machine Detection @
http://docs.oracle.com/javase/7/docs/tech‐
notes/guides/vm/server-class.html
-agentlib:libname[=options]
Load native agent library libname, e.g.
-agentlib:hprof
-agentlib:jdwp=help
-agentlib:hprof=help
For more information, see JVMTI Agent Command Line Options @
http://docs.oracle.com/javase/7/docs/plat‐
form/jvmti/jvmti.html#starting.
-agentpath:pathname[=options]
Load a native agent library by full pathname. For more informa‐
tion, see JVMTI Agent Command Line Options @
http://docs.oracle.com/javase/7/docs/plat‐
form/jvmti/jvmti.html#starting.
-classpath classpath
-cp classpath
Specify a list of directories, JAR archives, and ZIP archives to
search for class files. Class path entries are separated by
colons (:). Specifying -classpath or -cp overrides any setting of
the CLASSPATH environment variable.
If -classpath and -cp are not used and CLASSPATH is not set, the
user class path consists of the current directory (.).
As a special convenience, a class path element containing a base‐
name of * is considered equivalent to specifying a list of all
the files in the directory with the extension .jar or .JAR (a
java program cannot tell the difference between the two invoca‐
tions).
For example, if directory foo contains a.jar and b.JAR, then the
class path element foo/* is expanded to a A.jar:b.JAR, except
that the order of jar files is unspecified. All jar files in the
specified directory, even hidden ones, are included in the list.
A classpath entry consisting simply of * expands to a list of all
the jar files in the current directory. The CLASSPATH environment
variable, where defined, will be similarly expanded. Any class‐
path wildcard expansion occurs before the Java virtual machine is
started -- no Java program will ever see unexpanded wildcards
except by querying the environment. For example; by invoking Sys‐
tem.getenv("CLASSPATH").
For more information on class paths, see Setting the Class Path @
http://docs.oracle.com/javase/7/docs/tech‐
notes/tools/index.html#classpath.
-Dproperty=value
Set a system property value.
-d32
-d64
Request that the program to be run in a 32-bit or 64-bit environ‐
ment, respectively. If the requested environment is not installed
or is not supported, an error is reported.
Currently only the Java HotSpot Server VM supports 64-bit opera‐
tion, and the "-server" option is implicit with the use of -d64.
And the "-client" option is ignored with the use of -d64. This is
subject to change in a future release.
If neither -d32 nor -d64 is specified, the default is to run in a
32-bit environment, except for 64-bit only systems. This is sub‐
ject to change in a future release.
-enableassertions[:<package name>"..." | :<class name> ]
-ea[:<package name>"..." | :<class name> ]
-disableassertions[:<package name>"..." | :<class name> ]
-da[:<package name>"..." | :<class name> ]
Disable assertions. This is the default.
With no arguments, disableassertions or -da disables assertions.
With one argument ending in "...", the switch disables assertions
in the specified package and any subpackages. If the argument is
simply "...", the switch disables assertions in the unnamed pack‐
age in the current working directory. With one argument not end‐
ing in "...", the switch disables assertions in the specified
class.
To run a program with assertions enabled in package com.wom‐
bat.fruitbat but disabled in class com.wombat.fruitbat.Brickbat,
the following command could be used:
java -ea:com.wombat.fruitbat... -da:com.wombat.fruitbat.Brickbat <Main Class>
The -disableassertions and -da switches apply to all class load‐
ers and to system classes (which do not have a class loader).
There is one exception to this rule: in their no-argument form,
the switches do not apply to system. This makes it easy to turn
on asserts in all classes except for system classes. A separate
switch is provided to enable asserts in all system classes; see
-disablesystemassertions below. Enable assertions. Assertions
are disabled by default.
With no arguments, enableassertions or -ea enables assertions.
With one argument ending in "...", the switch enables assertions
in the specified package and any subpackages. If the argument is
simply "...", the switch enables assertions in the unnamed pack‐
age in the current working directory. With one argument not end‐
ing in "...", the switch enables assertions in the specified
class.
If a single command line contains multiple instances of these
switches, they are processed in order before loading any classes.
So, for example, to run a program with assertions enabled only in
package com.wombat.fruitbat (and any subpackages), the following
command could be used:
java -ea:com.wombat.fruitbat... <Main Class>
The -enableassertions and -ea switches apply to all class loaders
and to system classes (which do not have a class loader). There
is one exception to this rule: in their no-argument form, the
switches do not apply to system. This makes it easy to turn on
asserts in all classes except for system classes. A separate
switch is provided to enable asserts in all system classes; see
-enablesystemassertions below.
-enablesystemassertions
-esa
Enable asserts in all system classes (sets the default assertion
status for system classes to true).
-disablesystemassertions
-dsa
Disables asserts in all system classes.
-help or -?
Display usage information and exit.
-jar
Execute a program encapsulated in a JAR file. The first argument
is the name of a JAR file instead of a startup class name. In
order for this option to work, the manifest of the JAR file must
contain a line of the form Main-Class: classname. Here, classname
identifies the class having the pub‐
lic static void main(String[] args) method that serves as your
application's starting point. See the jar(1) and the Jar trail of
the Java Tutorial @
http://docs.oracle.com/javase/tutorial/deployment/jar for infor‐
mation about working with Jar files and Jar-file manifests.
When you use this option, the JAR file is the source of all user
classes, and other user class path settings are ignored.
Note that JAR files that can be run with the "java -jar" option
can have their execute permissions set so they can be run without
using "java -jar". Refer to Java Archive (JAR) Files @
http://docs.oracle.com/javase/7/docs/tech‐
notes/guides/jar/index.html.
-javaagent:jarpath[=options]
Load a Java programming language agent, see java.lang.instrument
@
http://docs.oracle.com/javase/7/docs/api/java/lang/instru‐
ment/package-summary.html.
-jre-restrict-search
Include user-private JREs in the version search.
-no-jre-restrict-search
Exclude user-private JREs in the version search.
-showversion
Display version information and continue. (See also -version.)
-splash:imagepath
Show splash screen with image specified by imagepath.
-verbose
-verbose:class
Display information about each class loaded.
-verbose:gc
Report on each garbage collection event.
-verbose:jni
Report information about use of native methods and other Java
Native Interface activity.
-version
Display version information and exit. (See also -showversion.)
-version:release
Specifies that the version specified by release is required by
the class or jar file specified on the command line. If the ver‐
sion of the java command invoked does not meet this specification
and an appropriate implementation is found on the system, the
appropriate implementation will be used.
release not only can specify an exact version, but can also spec‐
ify a list of versions called a version string. A version string
is an ordered list of version ranges separated by spaces. A ver‐
sion range is either a version-id, a version-id followed by a
star (*), a version-id followed by a plus sign (+) , or two ver‐
sion-ranges combined using an ampersand (&). The star means pre‐
fix match, the plus sign means this version or greater, and the
ampersand means the logical anding of the two version-ranges. For
example:
-version:"1.6.0_13 1.6*&1.6.0_10+"
The meaning of the above is that the class or jar file requires
either version 1.6.0_13, or a version with 1.6 as a version-id
prefix and that is not less than 1.6.0_10.. The exact syntax and
definition of version strings may be found in Appendix A of the
Java Network Launching Protocol & API Specification (JSR-56).
For jar files, the usual preference is to specify version
requirements in the jar file manifest rather than on the command
line.
See the following NOTES section for important policy information
on the use of this option.
Non-Standard Options
-X Display information about non-standard options and exit.
-Xint
Operate in interpreted-only mode. Compilation to native code is
disabled, and all bytecodes are executed by the interpreter. The
performance benefits offered by the Java HotSpot VMs' adaptive
compiler will not be present in this mode.
-Xbatch
Disable background compilation. Normally the VM will compile the
method as a background task, running the method in interpreter
mode until the background compilation is finished. The -Xbatch
flag disables background compilation so that compilation of all
methods proceeds as a foreground task until completed.
-Xbootclasspath:bootclasspath
Specify a colon-separated list of directories, JAR archives, and
ZIP archives to search for boot class files. These are used in
place of the boot class files included in the Java platform JDK.
Note: Applications that use this option for the purpose of over‐
riding a class in rt.jar should not be deployed as doing so would
contravene the Java Runtime Environment binary code license.
-Xbootclasspath/a:path
Specify a colon-separated path of directires, JAR archives, and
ZIP archives to append to the default bootstrap class path.
-Xbootclasspath/p:path
Specify a colon-separated path of directires, JAR archives, and
ZIP archives to prepend in front of the default bootstrap class
path. Note: Applications that use this option for the purpose of
overriding a class in rt.jar should not be deployed as doing so
would contravene the Java Runtime Environment binary code
license.
-Xcheck:jni
Perform additional checks for Java Native Interface (JNI) func‐
tions. Specifically, the Java Virtual Machine validates the
parameters passed to the JNI function as well as the runtime
environment data before processing the JNI request. Any invalid
data encountered indicates a problem in the native code, and the
Java Virtual Machine will terminate with a fatal error in such
cases. Expect a performance degradation when this option is used.
-Xfuture
Perform strict class-file format checks. For purposes of back‐
wards compatibility, the default format checks performed by the
JDK's virtual machine are no stricter than the checks performed
by 1.1.x versions of the JDK software. The -Xfuture flag turns on
stricter class-file format checks that enforce closer conformance
to the class-file format specification. Developers are encouraged
to use this flag when developing new code because the stricter
checks will become the default in future releases of the Java
application launcher.
-Xnoclassgc
Disable class garbage collection. Use of this option will prevent
memory recovery from loaded classes thus increasing overall mem‐
ory usage. This could cause OutOfMemoryError to be thrown in some
applications.
-Xincgc
Enable the incremental garbage collector. The incremental garbage
collector, which is off by default, will reduce the occasional
long garbage-collection pauses during program execution. The
incremental garbage collector will at times execute concurrently
with the program and during such times will reduce the processor
capacity available to the program.
-Xloggc:file
Report on each garbage collection event, as with -verbose:gc, but
log this data to file. In addition to the information -verbose:gc
gives, each reported event will be preceeded by the time (in sec‐
onds) since the first garbage-collection event.
Always use a local file system for storage of this file to avoid
stalling the JVM due to network latency. The file may be trun‐
cated in the case of a full file system and logging will continue
on the truncated file. This option overrides -verbose:gc if both
are given on the command line.
-Xmnsize or -XX:NewSize
Sets the size of the young generation (nursery).
-Xmsn
Specify the initial size, in bytes, of the memory allocation
pool. This value must be a multiple of 1024 greater than 1MB.
Append the letter k or K to indicate kilobytes, or m or M to
indicate megabytes. The default value is chosen at runtime based
on system configuration. For more information, see HotSpot
Ergonomics @
http://docs.oracle.com/javase/7/docs/tech‐
notes/guides/vm/gc-ergonomics.html
Examples:
-Xms6291456
-Xms6144k
-Xms6m
-Xmxn
Specify the maximum size, in bytes, of the memory allocation
pool. This value must a multiple of 1024 greater than 2MB. Append
the letter k or K to indicate kilobytes, or m or M to indicate
megabytes. The default value is chosen at runtime based on system
configuration. For more information, see HotSpot Ergonomics @
http://docs.oracle.com/javase/7/docs/tech‐
notes/guides/vm/gc-ergonomics.html
Examples:
-Xmx83886080
-Xmx81920k
-Xmx80m
On Solaris 7 and Solaris 8 SPARC platforms, the upper limit for
this value is approximately 4000m minus overhead amounts. On
Solaris 2.6 and x86 platforms, the upper limit is approximately
2000m minus overhead amounts. On Linux platforms, the upper limit
is approximately 2000m minus overhead amounts.
-Xprof
Profiles the running program, and sends profiling data to stan‐
dard output. This option is provided as a utility that is useful
in program development and is not intended to be used in produc‐
tion systems.
-Xrs
Reduces use of operating-system signals by the Java virtual
machine (JVM).
In a previous release, the Shutdown Hooks facility was added to
allow orderly shutdown of a Java application. The intent was to
allow user cleanup code (such as closing database connections) to
run at shutdown, even if the JVM terminates abruptly.
Sun's JVM catches signals to implement shutdown hooks for abnor‐
mal JVM termination. The JVM uses SIGHUP, SIGINT, and SIGTERM to
initiate the running of shutdown hooks.
The JVM uses a similar mechanism to implement the pre-1.2 feature
of dumping thread stacks for debugging purposes. Sun's JVM uses
SIGQUIT to perform thread dumps.
Applications embedding the JVM frequently need to trap signals
like SIGINT or SIGTERM, which can lead to interference with the
JVM's own signal handlers. The -Xrs command-line option is avail‐
able to address this issue. When -Xrs is used on Sun's JVM, the
signal masks for SIGINT, SIGTERM, SIGHUP, and SIGQUIT are not
changed by the JVM, and signal handlers for these signals are not
installed.
There are two consequences of specifying -Xrs:
o SIGQUIT thread dumps are not available.
o User code is responsible for causing shutdown hooks to run, for
example by calling System.exit() when the JVM is to be termi‐
nated.
-Xssn
Set thread stack size.
-XX:AllocationPrefetchStyle=n
Sets the style of prefetch used during allocation. default=2.
-XX:+AggressiveOpts
Enables aggressive optimization.
-XX:+|-DisableAttachMechanism
This option specifies whether tools (such as jmap and jconsole)
are allowed to attach to the JVM. By default, this feature is
disabled. That is, attaching is enabled. Example usage:
java -XX:+DisableAttachMechanism
-XXLargePageSizeInBytes=n
This option specifies the maximum size for large pages.
-XX:MaxGCPauseMillis=n
Sets a target for the maximum GC pause time.
This is a soft goal, and the JVM will make its best effort to
achieve it.
-XX:NewSize
Sets the size of the young generation (nursery). Sames as -Xmn‐
size.
-XX:ParallelGCThreads=n
Sets the number of GC threads in the parallel collectors.
-XX:PredictedClassLoadCount=n
This option requires that the UnlockExperimentalVMOptions flag be
set first. Use the PredictedClassLoadCount flag if your applica‐
tion loads a lot of classes, and especially if class.forName() is
used heavily. The recommended value is the number of classes
loaded as shown in the output from -verbose:class.
Example usage:
java -XX:+UnlockExperimentalVMOptions -XX:PredictedClassLoadCount=60013
-XX:+PrintCompilation
Prints verbose output from the HotSpot dynamic runtime compiler.
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps
Prints garbage collection output along with time stamps.
-XX:SoftRefLRUPolicyMSPerMB=0
This flag enables aggressive processing of software references.
Use this flag if HotSpot GC is impacted by the software reference
count.
-XX:TLABSize=n
Thread local allocation buffers (TLAB) are enabled by default in
HotSpot. HotSpot automatically sizes TLABs based on allocation
patterns. The -XX:TLABSize option allows fine-tuning the size of
TLABs.
-XX:+UseAltSigs
The VM uses SIGUSR1 and SIGUSR2 by default, which can sometimes
conflict with applications that signal-chain SIGUSR1 and SIGUSR2.
The -XX:+UseAltSigs option will cause the VM to use signals other
than SIGUSR1 and SIGUSR2 as the default.
-XX:+|-UseCompressedOops
Enables compressed references in 64-bit JVMs.
This option is true by default.
-XX:+UseConcMarkSweepGC or -XX:+UseG1GC
These flags enable either the Concurrent Mark Sweep (CMS) or the
G1 garbage collectors.
-XX:+|-UseLargePages
Use this flag to enable large page support. Large pages are
enabled by default on Solaris.
-XX:+UseParallelOldGC
Enables the parallel garbage collectors, which are optimized for
throughput and average response time.
NOTES
The -version:release command line option places no restrictions on the
complexity of the release specification. However, only a restricted
subset of the possible release specifications represent sound policy
and only these are fully supported. These policies are:
1. Any version, represented by not using this option.
2. Any version greater than an arbitrarily precise version-id. For
example:
"1.6.0_10+"
This would utilize any version greater than 1.6.0_10. This is
useful for a case where an interface was introduced (or a bug
fixed) in the release specified.
3. A version greater than an arbitrarily precise version-id, bounded
by the upper bound of that release family. For example:
"1.6.0_10+&1.6*"
4. "Or" expressions of items 2. or 3. above. For example:
"1.6.0_10+&1.6* 1.7+"
Similar to item 2. this is useful when a change was introduced in
a release (1.7) but also made available in updates to previous
releases.
EXIT STATUS
The following exit values are generally returned by the launcher, typi‐
cally when the launcher is called with the wrong arguments, serious
errors, or exceptions thrown from the Java Virtual Machine. However, a
Java application may choose to return any value using the API call Sys‐
tem.exit(exitValue).
o 0: Successful completion
o >0: An error occurred
SEE ALSO
o javac(1)
o jdb(1)
o javah(1)
o jar(1)
o The Java Extensions Framework @
http://docs.oracle.com/javase/7/docs/technotes/guides/exten‐
sions/index.html
o Security Features @
http://docs.oracle.com/javase/7/docs/technotes/guides/secu‐
rity/index.html.
o HotSpot VM Specific Options @
http://java.sun.com/docs/hotspot/VMOptions.html.
20 Mar 2012 java(1)
